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Comment by scythe | Hacker News Reader

Surprisingly, it's one of the (very) few cases where not building the subway was the right idea in the long run, because of the magnitude-9 earthquake risk the region faces that wasn't known about in 1965. A subway could be built today, but an elevated rail system would be safer, according to my limited understanding of earthquake safety.

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I'm pretty sure the opposite is true -- below ground structures are more resistant to earthquakes. Earthquake concerns are the primary reason the above ground SR-99 viaduct is being torn down and replaced with a below ground tunnel.

But I do agree that if they had built a tunnel 50 years ago, it definitely wouldn't have been designed to be resistant to a magnitude 9 earthquake.

Not trying to be cute or anything, but... Given the subduction zone, isn’t this like deciding which kind of non-skid pads to put on the deck chairs of the Titanic?

Kind of. There's a probabilistic argument that paying a certain amount for something that will survive a smaller earthquake is sometimes worth doing. As a nuclear reactor designer, we learn that there is, however, no upper limit to how strong an earthquake can be. Once the soil fails your statement is accurate; nothing's going to survive.

Surprisingly, tunnels have very good earthquake resistance. See http://www.wsdot.wa.gov/Projects/Viaduct/Status/Blog/tunnels....

Interesting. Would the safety of a tunnel depend on whether the most powerful pressure waves were traveling parallel with the tunnel or perpendicular to it?

That was an incredibly simple and effective explanation:

>Imagine a plate of fruit-filled gelatin dessert. Tunnels are like the pieces of fruit at the base of the gelatin, while above-ground structures are like the fruit toward the top. If you shake the plate, the movement becomes more exaggerated as it flows up from the base of the gelatin. In an earthquake, this translates to tunnel movement measured in inches, while the movement above ground might be measured in feet.

BART was completed in 1972 and survived a few earthquakes over the past few years just fine.

They have subways in Tokyo.

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